<!doctype html> 
<html> 
<head> 
    <meta charset="utf-8"> 
    <title></title> 
</head>
<body>

<script type="text/javascript">
var a;
alert(a);
/*
	function show(a){
		alert(a);//undefined
		var b;
		alert(a === b);//false;
	};

	show();

*/
</script>
</body>
</html>